Commit dc853e26 authored by Jiri Olsa's avatar Jiri Olsa Committed by Ingo Molnar

perf/x86/intel: Fix debug_store reset field for freq events

There's a bug in PEBs event enabling code, that prevents PEBS
freq events to work properly after non freq PEBS event was run.

freq events - perf_event_attr::freq set
              -F <freq> option of perf record

PEBS events - perf_event_attr::precise_ip > 0
              default for perf record

Like in following example with CPU 0 busy, we expect ~10000 samples
for following perf tool run:

  # perf record -F 10000 -C 0 sleep 1
  [ perf record: Woken up 2 times to write data ]
  [ perf record: Captured and wrote 0.640 MB perf.data (10031 samples) ]

Everything's fine, but once we run non freq PEBS event like:

  # perf record -c 10000 -C 0 sleep 1
  [ perf record: Woken up 4 times to write data ]
  [ perf record: Captured and wrote 1.053 MB perf.data (20061 samples) ]

the freq events start to fail like this:

  # perf record -F 10000 -C 0 sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.185 MB perf.data (40 samples) ]

The issue is in non freq PEBs event initialization of debug_store reset
field, which value is used to auto-reload the counter value after PEBS
event drain. This value is not being used for PEBS freq events, but once
we run non freq event it stays in debug_store data and screws the
sample_freq counting for PEBS freq events.

Setting the reset field to 0 for freq events.
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170714163551.19459-1-jolsa@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent dd0b06b5
...@@ -895,6 +895,8 @@ void intel_pmu_pebs_enable(struct perf_event *event) ...@@ -895,6 +895,8 @@ void intel_pmu_pebs_enable(struct perf_event *event)
if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) { if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) {
ds->pebs_event_reset[hwc->idx] = ds->pebs_event_reset[hwc->idx] =
(u64)(-hwc->sample_period) & x86_pmu.cntval_mask; (u64)(-hwc->sample_period) & x86_pmu.cntval_mask;
} else {
ds->pebs_event_reset[hwc->idx] = 0;
} }
} }
......
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